Of the various types of irrigation equipment that has been utilized for extensive periods of time, mobile irrigation systems that rotate about a central point or water supply tower for the purpose of irrigating large generally circular land areas are well known in the art as indicated by U.S. Pat. No. 3,314,608 to Curtis et al. Generally there is provided a centrally located tower that serves as a pivot for the rotatable irrigation apparatus and also serves to supply water to the irrigation apparatus through a conventional swivel connection. The irrigation apparatus will generally comprise a plurality of spans, each span being supported by one or more mobile support structures that travel over the land area. Each of the mobile support devices typically comprises a framework of generally triangular nature with the water supply pipe of the irrigation system being supported by the framework. The framework also typically defines an elongated base typically having a pair of ground contacting elements such as wheels, tracks, etc. that are supported at each extremity of the base in order to provide both mobile support and stability for the framework defining the mobile base. While it is intended that the present invention be of sufficient breadth to include all manner of ground engaging motive devices such as wheels, tracks, etc., for purposes of simplicity the ground engaging elements will be referred to as "wheels".
Since overhead mobile irrigation systems of this nature are very expensive and since it may be desirable to move the irrigation system to other land areas in order to increase the amount of land area that is under irrigation and therefore render the irrigation process more commercially feasible, it is considered desirable to provide each of the mobile bases of such irrigation systems with wheels or other ground contacting elements that are rotatable from an operative position, where they are disposed substantially normal to the direction of the water supply pipe of each of the spans, to a system movement or towing positing where the wheels or ground contacting elements are disposed in substantially parallel relationship to the water supply pipe. In order to accomplish such movement, each of the wheels must be rotatable through an arc of substantially 90.degree.. It is also well known in the art to provide for simple 90.degree. rotation of ground engaging wheels and other drive elements as shown in U.S. Pat. No. 3,662,776 to Bryant et al, which shows a bolting arrangement allowing the drive unit supporting the wheel to be swung relative to the support frame to position the wheels axis substantially parallel to the conduit or at a substantial angle relative thereto. The bolts provide for locking of the drive unit in either position. Likewise U.S. Pat. No. 3,771,719 to Raso et al teaches the provision of a drive and gear module that is provided with a quick disconnecting device in order to permit wheel rotation for towing.
Where the drive wheels are disposed in substantially parallel relation with the elongated mobile base to which they are connected during irrigation operations, which is typically the case, the wheels are disposed in offset relation to a center line of the irrigation system that extends from the pivot of each of the spans centrally through the mobile support structure at the extremity of each of the spans. In essence, each of the ground contacting wheels are disposed in tangential relation to an arc defined by the intersection of the imaginary centerline of the irrigation system with the mobile base. There is a tendency for the ground engaging wheels to roll in a straight line over the land area, but the force on each of the spans of the irrigation system caused by the restraining presence of the pivot tower and water supply system causes the ground engaging wheels to be forced sideways or scrubbed along the ground surface. This sidewise movement or scrubbing effect greatly accelerates wear on the ground engaging wheels and severely detracts from the useful operating life thereof. Where the ground engaging wheels are defined by rubber tires, the tire treads will be caused to wear quite rapidly by the scrubbing effect thereof with the land surface. Where the ground engaging elements are defined by devices other than tires, such as tracks, metal wheels, etc., there is considerable stress induced by the nature of the contact of the ground engaging elements with the land surface which stress has a damaging effect both on the ground contacting elements and the drive systems connected thereto and to the irrigation system itself. It is desirable therefore to provide means for causing the wheels or ground contacting elements of the irrigation system to precisely track a circular course in order to eliminate any scrubbing or dragging effect thereof as a circular course is circumscribed during irrigation operations.
It is therefore a primary feature of the present invention to provide a novel mobile base construction for overhead irrigation apparatus adapted for circular movement about a centrally located point, wherein each of the various wheels or ground contacting elements of the mobile base is precisely oriented so as to circumscribe a circular track as the irrigation system is rotated regardless of the particular distance of wheel location from the central point of rotation of the irrigation system.
It is a further feature of the present invention to provide a novel mobile base construction for irrigation systems that are rotatable about a centrally located point, wherein each of the wheels or ground contacting elements of the irrigation system are disposed in offset relation with respect to the center line of the irrigation system and yet are oriented in such manner as to track a precise circle during irrigation operations.
Among the several objects of the present invention is contemplated the provision of a novel mobile base construction for irrigation systems that are rotatable about a centrally located point, wherein each of the wheels or ground contacting elements of the irrigation system may be simply and efficiently positioned either at an operative position where the ground engaging wheels or elements subscribe a circular arc or a movement position where the wheels or ground contacting elements are disposed in substantially parallel relation with the elongated axis of the irrigation system to facilitate linear movement thereof from place to place.
It is also a feature of the present invention to provide a novel mobile base construction for overhead irrigation systems of the circular movement type, whereby means is employed to positively establish the operative and movement positions of the wheels or ground contacting elements so as to simplify repositioning of the wheels or ground contacting elements following either operation or movement of the irrigation system.
It is among the several objects of the present invention to provide a novel overhead irrigation system adapted for rotary movement, whereby a single position controlling element may be utilized for establishing positioning of the wheels or ground contacting elements either in the operative or movement positions thereof.
It is an even further feature of the present invention to provide a novel overhead irrigation system adapted for rotary movement, whereby a single type of position adjustment device may be employed to establish positioning of all of the various wheels or ground contacting elements of the irrigation system, there being provided simple means for wheel adjustment in order to precisely establish the various operative and movement positions of the various wheels of the irrigation system as desired.
It is another object of the present invention to provide a position controlling mechanism for the ground contacting elements of a traveling irrigation sprinkling system wherein the ground contacting elements will become repositioned at the proper adjusted operating position thereof immediately upon being moved from a towing position to the operating position thereof.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention. For example, although the present invention is described pricipally as it relates to utilization in conjunction with irrigation systems that are adapted for circular movement about a central point for irrigation of large generally circular land areas, it is not intended in any way to limit the present invention to this particular type of irrigation system. Wheel adjustment devices may be provided for use in connection with irrigation systems of other types if controllable wheel adjustment is appropriate.